Abstract: A process for monitoring defects in the material of a moving web of paper or defects in operations performed on the web of paper. An air brush spray head applies ink for a predetermined duration at a location along an edge of the moving web of paper during a press operation and after a predetermined period of time to indicate that a defect has passed. A scanner senses the ink during a subsequent collating operation so that the process line can be stopped and the defect corrected. The location of the ink on the web of paper is at a point wherein the defect has passed and good material is present.